Wright dykes : a geochemical study of the dyke-forming rock types of the Wright Valley, Southern Victoria Land, Antarctica
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THE BASEMENT COMPLEX OF THE WRIGHT VALLEY IS CROSS-CUT BY SEVERAL HUNDRED DYKES OF VARYING AND WIDE RANGING LITHOLOGIES. THE MAJORITY ARE CONCENTRATED-IN TWO SWARMS, LOCATED NEAR MOUNT LOKE, IN THE LOWER WRIGHT VALLEY AND LAKE VANDA, IN THE UPPER WRIGHT VALLEY. THESE SWARMS ARE PART OF A NORTH-EAST STRIKING COMPLEX WHICH FORMS SUB-PARALLEL BELTS THROUGHOUT THE DRY VALLEY REGION. THE MAJORITY OF DYKES WITHIN THE WRIGHT VALLEY WERE EMPLACED AT SHALLOW LEVELS WITHIN THE CRUST. THE DYKES FORM PART OF THE GRANITE HARBOUR INTRUSIVES (GRINDLEY AND WARREN, 1 964).
DYKES WITHIN THE WRIGHT VALLEY FALL INTO THREE DISTINCT ASSOCIATIONS, ARE OF AN OROGENIC NATURE, AND INCLUDE SUITES OF HIGH-K CALC-ALKALINE TO SHOSHONITIC AFFINITY. K I AR AND RB I SR DETERMINATIONS BY PREVIOUS WORKERS SUGGEST EMPLACEMENT AGE IS PROBABLY NOT YOUNGER THAN 460 MA. DYKE ORIENTATIONS OF THE LATTER TWO SUITES ARE WELL CORRELATED WITH OBSERVED FAULT TRACES.
THE FIRST SUITE COMPRISES HIGH-K CALC-ALKALINE HORNBLENDE-BIOTITE DIORITE DYKES WHICH OCCUR PREDOMINANTLY WITHIN THE MOUNT LOKE REGION. THEY FORM THE EARLIEST NON-DEFORMED DYKE INTRUSIVES WITHIN THE WRIGHT VALLEY. THE ORIGINS OF THIS SUITE REMAIN UNCLEAR.
THE SECOND SUITE IS REPRESENTED BY HIGH-K CALC-ALKALINE MONZODIORITE, GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES. THE MONZODIORITE DYKES OCCUR ONLY AT LAKE VANDA, WHILE THE GRANODIORITE AND GRANITE DYKES OCCUR THROUGHOUT THE VALLEY. THE MONZODIORITE MAGMA HAS EVOLVED BY FRACTIONAL CRYSTALLISATION OF A BASIC MAGMA.
THE THIRD SUITE IS REPRESENTED BY ABSAROKITE, SHOSHONITE, BANAKITE, GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES. THE ABSAROKITE, SHOSHONITE AND BANAKITE DYKES OCCUR ONLY WITHIN THE MOUNT LOKE REGION WHILE THE GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES OCCUR PREDOMINANTLY WITHIN THE LAKE VANDA REGION. SEVERAL OF THE ABSAROKITE DYKES ARE PRIMARY MAGMAS PRODUCED BY PARTIAL MELTING OF A MANTLE SOURCE REGION(S) ENRICHED IN INCOMPATIBLE ELEMENTS. PRIMARY MAGMA AS DYKES AT SHALLOW CRUSTAL LEVELS IMPLIES THE PRESENCE OF DEEP LITHOSPHERIC FRACTURES. A COMPOSITE DYKE COMPRISING GRANODIORITE CORE AND SHOSHONITE MARGINS LEAD TO THE CONCLUSION THAT THE SHOSHONITE AND BANAKITE DYKES ARE HYBRID IN ORIGIN, THE RESULT OF MIXING BETWEEN ABSAROKITE AND GRANODIORITE MAGMAS. ALL GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES WITHIN THE VALLEY SHOW I-TYPE AFFINITIES AND POSSESS AN OVERALL METALUMINOUS CHARACTER. THESE MAGMAS WERE GENERATED AT THE BASE OF THE CRUST BY THE INTERACTION OF A MANTLE MELT AND A CRUSTAL COMPONENT AND SUCCESSIVELY EVOLVED BY FRACTIONAL CRYSTALLISATION OF ALKALI FELDSPAR.
DYKE INTRUSIVES WITHIN THE WRIGHTVALLEY AND GREATER DRY VALLEY REGION WERE EMPLACED IN A POST-COLLISIONAL EXTENSIONAL REGIME ASSOCIATED WITH THE INCIPIENT BACK-ARC SPREADING REPRESENTING THE FINAL STAGES OF A CAMBRO-ORDOVICIAN OROGENIC CYCLE.
DYKES WITHIN THE WRIGHT VALLEY FALL INTO THREE DISTINCT ASSOCIATIONS, ARE OF AN OROGENIC NATURE, AND INCLUDE SUITES OF HIGH-K CALC-ALKALINE TO SHOSHONITIC AFFINITY. K I AR AND RB I SR DETERMINATIONS BY PREVIOUS WORKERS SUGGEST EMPLACEMENT AGE IS PROBABLY NOT YOUNGER THAN 460 MA. DYKE ORIENTATIONS OF THE LATTER TWO SUITES ARE WELL CORRELATED WITH OBSERVED FAULT TRACES.
THE FIRST SUITE COMPRISES HIGH-K CALC-ALKALINE HORNBLENDE-BIOTITE DIORITE DYKES WHICH OCCUR PREDOMINANTLY WITHIN THE MOUNT LOKE REGION. THEY FORM THE EARLIEST NON-DEFORMED DYKE INTRUSIVES WITHIN THE WRIGHT VALLEY. THE ORIGINS OF THIS SUITE REMAIN UNCLEAR.
THE SECOND SUITE IS REPRESENTED BY HIGH-K CALC-ALKALINE MONZODIORITE, GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES. THE MONZODIORITE DYKES OCCUR ONLY AT LAKE VANDA, WHILE THE GRANODIORITE AND GRANITE DYKES OCCUR THROUGHOUT THE VALLEY. THE MONZODIORITE MAGMA HAS EVOLVED BY FRACTIONAL CRYSTALLISATION OF A BASIC MAGMA.
THE THIRD SUITE IS REPRESENTED BY ABSAROKITE, SHOSHONITE, BANAKITE, GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES. THE ABSAROKITE, SHOSHONITE AND BANAKITE DYKES OCCUR ONLY WITHIN THE MOUNT LOKE REGION WHILE THE GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES OCCUR PREDOMINANTLY WITHIN THE LAKE VANDA REGION. SEVERAL OF THE ABSAROKITE DYKES ARE PRIMARY MAGMAS PRODUCED BY PARTIAL MELTING OF A MANTLE SOURCE REGION(S) ENRICHED IN INCOMPATIBLE ELEMENTS. PRIMARY MAGMA AS DYKES AT SHALLOW CRUSTAL LEVELS IMPLIES THE PRESENCE OF DEEP LITHOSPHERIC FRACTURES. A COMPOSITE DYKE COMPRISING GRANODIORITE CORE AND SHOSHONITE MARGINS LEAD TO THE CONCLUSION THAT THE SHOSHONITE AND BANAKITE DYKES ARE HYBRID IN ORIGIN, THE RESULT OF MIXING BETWEEN ABSAROKITE AND GRANODIORITE MAGMAS. ALL GRANODIORITE, GRANITE AND LEUCOGRANITE DYKES WITHIN THE VALLEY SHOW I-TYPE AFFINITIES AND POSSESS AN OVERALL METALUMINOUS CHARACTER. THESE MAGMAS WERE GENERATED AT THE BASE OF THE CRUST BY THE INTERACTION OF A MANTLE MELT AND A CRUSTAL COMPONENT AND SUCCESSIVELY EVOLVED BY FRACTIONAL CRYSTALLISATION OF ALKALI FELDSPAR.
DYKE INTRUSIVES WITHIN THE WRIGHTVALLEY AND GREATER DRY VALLEY REGION WERE EMPLACED IN A POST-COLLISIONAL EXTENSIONAL REGIME ASSOCIATED WITH THE INCIPIENT BACK-ARC SPREADING REPRESENTING THE FINAL STAGES OF A CAMBRO-ORDOVICIAN OROGENIC CYCLE.
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1991Keiller
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Citation
Keiller, Ian Graham, 1965-, “Wright dykes : a geochemical study of the dyke-forming rock types of the Wright Valley, Southern Victoria Land, Antarctica,” Otago Geology Theses, accessed April 23, 2025, https://theses.otagogeology.org.nz/items/show/254.